I have two species of cory cats. One species is now showing strange markings that appear to be bite marks or perhaps a growth. Both of the Corys of that species are showing the same marks. Both of them have the marks on either side of their head. Both in nearly the same location of the head. The marks showed up on the Corys within days of each other and the marks have slowly gotten larger.

Because of the "regularity" of the marks, I am not so sure it's disease related. Perhaps spawning? Another fish? I do have angels in the tank, but they are small and I have never seen them pick on other fish. I also have another Cory of a different species who doesn't exhibit this mark.

Since the marks have shown up, they have spent a lot of time together, swimming closely together.